Background: The roles of host-specific versus viral-specific factors in determining inflammatory responses in the lung to acute viral infection remain unclear. We examined the role of age, sex and type of virus in determining the inflammatory responses to acute viral infection using a mouse model.

Methods: We infected BALB/c mice of both sexes with 104.5 pfu flu (A/ Memphis/1/71 H3N2) or 5 × 106 TCID50 RV (RV1b serotype). Bronchoalveolar lavage (BAL) samples were taken from groups of mice through the acute phase of infection and following recovery. BALs were used to ascertain total cell counts (TCC) and differential cell counts (macrophages: mac, neutrophils: neut) under light microscopy.

Results: Inflammatory responses were more severe and prolonged in mice inoculated with flu compared to those inoculated with RV. Both male and female flu inflammatory responses peaked at day 4, but females had significantly higher responses (TCC, p = 0.001; mac, p = 0.003; and neut p = 0.008). In contrast, the peak of TCC differed between sexes inoculated with RV (female D2; male D4), whereas the pattern of neutrophilic inflammation was the same. The magnitude of the response was the same between sexes (TCC, p = 0.71; mac, p = 0.52; neut, p = 0.3).

Conclusions: These data clearly demonstrate that host-specific and virus-specific effects are important in the inflammatory responses in the mouse lung.